A two-compartment exploratory model to study anxiolytic/anxiogenic effects of drugs in the rat

The response of a recently described light/dark choice novelty situation to anxiolytic and non-anxiolytic agents as well as to putative anxiogenic drugs was assessed in rats. Diazepam (1.0-10.0 mg/kg, i.p.), chlordiazepoxide (2.5-10.0 mg/kg, i.p.), and pentobarbital (pentobarbitone) (7.5-15.0 mg/kg, i.p.) enhanced rats' activity in the dark and brightly lit compartments as well as crossings between the two, while imipramine (5-20 mg/kg, i.p.) had no effects. None of these drugs changed animal locomotion in activity cages. d-Amphetamine (1.5 mg/kg, i.p.) caused a significant increase in the three parameters used to measure rats' exploratory activity, but the effect was due to an increase in the general activity of the animal. No tolerance to the effects of diazepam developed after daily treatment with 5 mg/kg i.p. for 15 days. Non-sedative and non-convulsant doses of putative anxiogenic drugs such as yohimbine (2.5-5.0 mg/kg, i.p.), picrotoxin (2.0-4.0 mg/ml, i.p.) and ethyl-beta-carboline-3-carboxylate (2.5-5 mg/kg, i.p.) reduced the exploratory activity of rats in the dark compartment. The advantages and problems of using this test to identify anxiolytic and anxiogenic drugs are discussed.     

Discriminative stimulus effects of alprazolam and diazepam: generalization to benzodiazepines, antidepressants and buspirone

Rats in one group were trained to discriminate alprazolam (1.0mg/kg, i.p.) and in another group diazepam (3.0mg/kg, i.p.) from saline in a two-lever drug discrimination procedure. Food presentation occurred after 10 consecutive responses on the lever associated either with the training drug or with saline. Alprazolam, diazepam, lorazepam and chlor diazepoxide increased responding on the drug-associated lever in a comparable dose-related manner in both groups of rats: the relative order of potency was lorazepam >/= alprazolam > diazepam >/= chlordiazepoxide. Flumazenil (10.0mg/kg, i.p.) attenuated the effects of the training drugs. A range of doses of buspirone and four drugs having antidepressant properties (amitriptyline, fluoxetine, cericlamine, imipramine) then were studied in both groups of rats. All five drugs caused approximately 40% increases (group mean) in drug-appropriate responding in alprazolam-trained rats whereas only amitriptyline partially substituted for diazepam. The results indicate that alprazolam has interoceptive stimulus effects that overlap with the stimulus effects of diazepam, yet the effects of alprazolam may not be identical to those of diazepam because the antidepressant drugs and buspirone substituted partially for alprazolam but generally not for diazepam.     

Diazepam and muscimol blockade of the gastrointestinal motor disturbances induced by acoustic stress in dogs

The influence of various drugs on the gastric motor inhibition induced by acoustic stress (AS) was investigated in fasted dogs fitted with strain-gauge transducers implanted on the antrum and proximal jejunum at 10 and 80 cm from the pylorus respectively. Started 40-50 min after the last gastric migrating motor complex (MMC), a 1 h acoustic stress delayed by 75% the occurrence of the next gastric but not jejunal MMC and was associated with a 4-fold increase in plasma cortisol. This AS-induced inhibition of the gastric MMC cycle was abolished after previous administration of diazepam (0.2 and 0.5 mg/kg i.m.) or muscimol (10 micrograms/kg i.v.) and partially reduced by a lower dose of diazepam (0.1 mg/kg i.m.); in contrast, it was still present after either naloxone (0.1 mg/kg i.m.), phentolamine (0.2 mg/kg i.v.) or propranolol (0.1 mg/kg i.v.) treatment. This selective benzodiazepine or GABA agonist blockade of noise-induced gastric motor alteration supports the hypothesis that release of CRF may be responsible for the gastrointestinal motor effects induced by acoustic stress.     

Adenosinergic system is involved in development of diazepam tolerance in mice

In the present study the effect of adenosinergic system on the development of diazepam tolerance to motor disturbances in mice was investigated. Diazepam tolerance was obtained by administration of diazepam at a dose of 5.0 mg/kg, s.c. for ten consecutive days. On the 1st and the 10th day of the experiment motor impairments were measured in two behavioural tests: rota-rod and chimney test. We showed that acute diazepam injection produced significant motor impairments in mice and that effect was decreased by repeated diazepam treatment, confirming the development of tolerance to the motor impairing effect of diazepam. We demonstrated that adenosine A₁ and/or A_2A receptor agonists: CPA (0.025 and 0.05 mg/kg, i.p.), CGS 21680 (0.1 and 0.2 mg/kg, i.p.), NECA (0.005 and 0.01 mg/kg, i.p.) pretreatment with diazepam were able to attenuate the development of diazepam tolerance and adenosine receptor antagonists: DPCPX (1.0 and 3.0 mg/kg, i.p.), DMPX (3.0 and 6.0 mg/kg, i.p.) and caffeine (10.0 and 20.0 mg/kg, i.p.) induced the opposite effect. The most apparent effects were obtained by non-selective agonist (NECA) and antagonist (caffeine) of adenosine receptors. We conclude that adenosinergic system plays an important role in mechanisms underlying the development of benzodiazepine tolerance.     

Comparison of the effects of benzodiazepines and other anticonvulsant drugs on synthesis and utilization of 5-HT in mouse brain

Acute administration of clonazepam (0.5-8.0 mg/kg, i.p.), diazepam (2-32 mg/kg, i.p.), chlordiazepoxide (1-40 mg/kg, i.p.) or diphenylhydantoin (5-320 mg/kg, i.p.), caused a dose-related elevation of the concentrations of, 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan in whole mouse brain. Carbamazepine (5-100 mg/kg, i.p.), and phenobarbitone (10-80 mg/kg, i.p.) raised the concentrations of 5-HT and 5-HIAA in the brain, whereas flurazepam (5-80 mg/kg, i.p.) only elevated the level of 5-HIAA. After administration of L[G-3H]tryptophan (25 microCi, s.c.), clonazepam (4 mg/kg), diazepam (32 mg/kg, i.p.), chlordiazepoxide (40 mg/kg) or diphenylhydantoin (40 mg/kg), but not carbamazepine (50 mg/kg), flurazepam (40 mg/kg) or phenobarbitone (80 mg/kg), increased the content of labelled tryptophan in brain. However, administration of drugs did not alter the incorporation of the label into [3H]5-HT, suggesting that the synthesis of 5-HT was unaffected. When incorporation of [3H]tryptophan into [3H]5-HT was complete and the pool of labelled 5-HT was decreasing, clonazepam, diazepam, chlordiazepoxide and diphenylhydantoin elevated the content of [3H]5-HT in brain. Flurazepam, phenobarbitone and carbamazepine were without apparent effect. Calculation of the rate of utilization of 5-HT (Km) showed that all drugs, apart from flurazepam, reduced the utilization of 5-HT. Using the rate of disappearance of 5-HT after inhibition of tryptophan hydroxylase by p-chlorophenylalanine (PCPA), all drugs, except flurazepam, diphenylhydantoin and phenobarbitone, decreased the utilization of 5-HT. The major action of the anticonvulsant drugs on the function of 5-HT in brain appears to be a decrease in the utilization of 5-HT without altering synthesis.     

3-(Methoxycarbonyl)-amino-beta-carboline reduces both the sedative and anticonvulsant effects of diazepam

The intrinsic effects of the benzodiazepine receptor ligand beta-CMC (3-(methoxycarbonyl)-amino-beta-carboline) and its interaction with the anticonvulsant and sedative effects of diazepam were assessed. beta-CMC (100 mg/kg i.p.) significantly elevated seizure threshold to bicuculline. beta-CMC (10 mg/kg) failed to alter the anticonvulsant action of diazepam (5 mg/kg i.p.), but significantly attenuated diazepam's sedative effect. A higher dose of beta-CMC (40 mg/kg) did attenuate diazepam's anticonvulsant action. The data suggest that beta-CMC is a partial agonist at benzodiazepine receptors.     

Benzodiazepines reduce gastric ulcers induced in rats by stress.

1 The sedative and antiulcer effects of chlordiazepoxide (5 to 50 mg/kg) and lorazepam (0.25 to 2.5 mg/kg) were investigated in the rat. 2 Sedation was measured by recording locomotor activity in a holeboard. Ulceration of the glandular stomach was induced by a 2 h period of restrain at 4 degrees C. 3 Acutely, both drugs produced significant sedation at all doses; high doses only (chlordiazepoxide 10 and 50 mg/kg; lorazepam 2.5 mg/kg) produced a significant reduction in ulcer formation. 4 With chronic treatment, after 5 and 10 days administration of chlordiazepoxide (50 mg/kg), tolerance to sedation was observed without a similar change in antiulcer action. 5 Cimetidine (20 mg/kg) and atropine (0.2 mg/kg) decreased ulcer formation without causing sedation. 6 The antisecretory profile of chlordiazepoxide (2 x 10(-4) M), in the rat isolated gastric mucosa, resembled that of atropine (10(-7) M) rather than cimetidine (10(-5) M). 7 These observations suggest that the antiulcer effect of benzodiazepines probably results from a combination of sedative, anxiolytic and antisecretory actions.     

Anxiogenic-like action of caerulein,a CCK-8 receptor agonist,in the mouse: influence of acute and subchronic diazepam treatment

Summary Effects of caerulein, a cholecystokinin octapeptide (CCK-8) receptor agonist, on exploratory activity of mice were investigated. Exploratory and locomotor activity of animals were measured using elevated plus-maze and open field tests. The systemic administration of caerulein at nonsedative doses (100 ng/kg-1 µkg i. p.) resulted in a significant decrease in the exploratory activity of mice. This effect was completely blocked by proglumide, a CCK-8 antagonist (15 mg/kg i. p.), indicating the participation of CCK-8 receptors. Acute treatment with low doses (0.1–0.75 mg/kg i. p.) of diazepam did not attenuate the anxiogenic-like effect of caerulein, but at more high doses of diazepam the coadministration depressed locomotor activity in mice. After subchronic diazepam treatment (2.5 mg/kg once a day, 10 days, i.p.) tolerance was developed toward the sedative effect of diazepam, and 72 h after withdrawal of the drug the animals showed increased anxiety in the plus-maze test. 30 min after the last injection procedure the anxiogenic-like effect of caerulein (500 ng/kg i. p.) on exploration was absent in both diazepam or vehicle groups. However, 72 h after the last pretreatment injection caerulein (500 ng/kg i. p.) reduced significantly the exploratory activity in control group, whereas it was inactive after diazepam withdrawal. The results obtained in this study support the hypothesis that endogenous CCK-8 an CCK-8 receptors are involved in the neurochemistry of anxiety and the anxiolytic action of benzodiazepine tranquillizers. Send offprint requests to: J. Harro at the above address     

Effects of buspirone on fixed interval responding in rats

Buspirone is a novel anxiolytic which does not share the muscle relaxant, anticonvulsant and sedative properties of classical anxiolytics such as the benzodiazepines. Its effects in different animal models of anxiety are also variable. The present experiments investigated the effects of buspirone on a fixed interval 60 s schedule of reinforcement (FI). In experiment 1, four doses of buspirone (10, 3.3, 1.1 and 0.3 mg/kg, i.p.) and two doses of chlordiazepoxide (5 and 20 mg/kg, i.p.) were administered to separate groups of rats throughout acquisition of the FI task. In experiment 2, four doses of buspirone (1.1, 0.3, 0.1 and 0.03 mg/kg, i.p.) and a single dose of chlordiazepoxide (5 mg/kg, i.p.) were used. Chlordiazepoxide generally released responding. At higher doses (1.1 mg/kg and above) buspirone suppressed responding in the later parts of the FI interval. The effects of lower doses were variable but included some response release in the later parts of the FI interval. At no dose did buspirone release responding at the beginning of the FI interval. The experiments show that buspirone differs qualitatively as well as quantitatively from chlordiazepoxide and that current animal models based on behavioural inhibition may need to be used with considerable care if detection of novel anxiolytics is to be ensured.     

Effects of acute and repeated zolpidem treatment on pentylenetetrazole-induced seizure threshold and on locomotor activity: Comparison with diazepam

Zolpidem and diazepam are widely used drugs acting via benzodiazepine binding sites on GABA_A receptors. While diazepam is non-selective, zolpidem has a high affinity for α1-, and no affinity for α5-containing receptors. Several studies suggested that behavioral effects of zolpidem might be more similar to classical benzodiazepines than previously thought. To compare the sedative and anticonvulsant properties of these drugs and to evaluate the importance of GABA_A receptor subunits for development of tolerance during chronic treatment, we tested the effects of acute and repeated administration of zolpidem and diazepam on ambulatory locomotor activity (a measure of sedation) and on the threshold for myoclonic, clonic and tonic seizures in response to i.v. infusion of pentylenetetrazole (PTZ). Both drugs given acutely in doses 0.3, 1 and 3 mg/kg reduced locomotion, and in doses 1 and 3 mg/kg elevated the threshold for PTZ-induced seizures. The effects of zolpidem and diazepam on the tonic seizure threshold were greater than on myoclonus and clonic seizure threshold. Diazepam and zolpidem (3 mg/kg), given 18 or 42 h after repeated drug treatment (10 days, 5 mg/kg, twice daily), decreased the PTZ seizure threshold and increased the locomotor activity as compared to control mice, indicating development of tolerance to their anticonvulsant and sedative effects. After repeated treatment the PTZ seizure threshold was not different between the two drugs, while differences in sedation became larger than after the acute treatment. The results suggest that α5-containing GABA_A receptors are not crucial for the development of sedative and anticonvulsant tolerance.     

Similar effects of buspirone and chlordiazepoxide on a fixed interval schedule with long-term, low-dose administration

Buspirone is a novel anxiolytic which does not share the muscle relaxant, anticonvulsant and sedative properties of classical anxiolytics such as the benzodiazepines. Its effects on behavioural tests of anxiolytic action generally match those of classical anxiolytics provided a low dose is used. However, in a previous experiment, buspirone appeared to affect fixed interval responding in a way which differed qualitatively as well as quantitatively from the classical anxiolytic chlordiazepoxide. It takes as much as 2 weeks for the clinical effects of anxiolytics to develop, during which time the side effects of benzodiazepines undergo tolerance. We, therefore, decided to compare long-term pre-administration (60 days, three injections/day) of buspirone and chlordiazepoxide on learning of a fixed interval 60-s schedule. The doses were based on previous acute dose-response tests of hippocampal theta rhythm in freely moving animals. Buspirone (0.1 mg/ kg i.p.) and chlordiazepoxide (0.4 mg/kg i.p.) produced similar increases in responding, especially in the middle of acquisition of the fixed interval schedule. Consistent with our acute electrophysiological tests, the effects of 0.4 mg/kg chlordiazepoxide were somewhat larger than those of 0.1 mg/kg buspirone. These results suggest that the acute effects of buspirone, but probably not chlordiazepoxide, on fixed interval responding are contaminated by side effects which do not seriously affect the results with long-term administration. The effects of both novel and classical anxiolytics on control of hippocampal theta rhythm appear to predict the magnitude of their common anxiolytic effects and to be unrelated to their different side effects.     

Involvement of the "peripheral" benzodiazepine receptor type (omega 3) in the tolerance to the electroencephalographic effects of benzodiazepines in rats: comparison of diazepam and clonazepam

Rapid tolerance to the sedative effect of large doses of diazepam (10 mg/kg IV), but not of large doses of clonazepam (2 mg/kg IV) occurs in rats after 5 days of treatment on a once-a-day regimen. Electroencephalographic (EEG) studies show that such behavioral tolerance is associated with a decreased induction of spindle bursts and with an increased induction of 20-30 Hz waves (beta-like activity). Administration of clonazepam plus the agonist of the "peripheral" benzodiazepine receptor type (omega 3) Ro 5-4864 (4 mg/kg IV) for 5 days induces signs of behavioral and EEG tolerance to sedative effects of the benzodiazepine agonist. In animals treated for 5 days with diazepam plus the omega 3 antagonist PK 11195 (5 mg/kg IV), no signs of EEG and behavioral tolerance are observed. These results suggest that omega 3 type activation influences the development of rapid tolerance to the sedative effect of diazepam in rats.     

Evaluation of the Anticonvulsant and Anxiolytic Potentials of Methyl Jasmonate in Mice

Methyl jasmonate (MJ) is one of the most well-studied plant stress hormones belonging to the jasmonate family. Previous studies have shown that MJ potentiated pentobarbitone sleeping time and enhanced GABA-mediated inhibitory neurotransmission, suggesting potential benefits in disorders associated with hyperactivity of the brain. This study was carried out to evaluate whether MJ has anticonvulsant and anxiolytic properties in mice. The anticonvulsant effect was assessed based on the prevention of tonic-clonic seizures induced by chemoconvulsant agents in mice. The anxiolytic property was evaluated utilizing the elevated plus maze (EPM) and light/dark transition paradigms. The effect of MJ on spontaneous locomotor activity (SMA) was also assessed. Mice received intraperitoneal (i.p.) injections of MJ 30 min before the tests were carried out and diazepam (2 mg/kg, i.p.) was used as the reference drug. MJ (50–400 mg/kg) did not protect the mice against tonic-clonic convulsions induced by picrotoxin (10 mg/kg, i.p.) or strychnine (3 mg/kg, i.p.). However, MJ (100, 200, and 400 mg/kg) offered 20, 60, and 100% protection against pentylenetetrazole (100 mg/kg, i.p.)-induced convulsions. In a similar manner to diazepam (2 mg/kg), MJ (400 mg/kg) produced a marked sedative effect as shown by decreases in the number of lines crossed and the duration of ambulation in the open field test. In contrast to diazepam (2 mg/kg), MJ (5–50 mg/kg) did not show anxiolytic effects in the EPM and light/dark transition paradigms. These findings suggest that methyl jasmonate at high doses possessed anticonvulsant properties in the pentylenetetrazole animal model of epilepsy, but did not produce anxiolytic activity in mice.     

Pretreatment with diazepam suppresses the reduction in defensive freezing behavior induced by fluvoxamine in the conditioned fear stress paradigm in mice

The effects of the selective serotonin (5-hydroxytryptamine (5-HT)) reuptake inhibitor fluvoxamine, given alone or in combination with the benzodiazepine anxiolytic diazepam on the defensive freezing behavior of mice in the conditioned fear stress paradigm were examined. Fluvoxamine (5-20 mg/kg, i.p.) induced a dose-dependent reduction in freezing behavior. In contrast, while low doses of diazepam (0.125 and 0.25 mg/kg, i.p.) reduced the freezing behavior, such effects were not observed with high doses of diazepam (0.5 and 1 mg/kg, i.p.). In the combination study, fluvoxamine (20 mg/kg, i.p. ) did not reduce the freezing behavior in mice that had been pretreated with diazepam (0.125-1 mg/kg, i.p.). None of the doses of fluvoxamine and diazepam used in the present study had any effects on motor activity under non-stressed conditions. These results suggest that benzodiazepines may negatively influence the clinical efficacy of selective 5-HT reuptake inhibitors in the treatment of anxiety disorders.     

The new antiepileptic drug levetiracetam normalises chlordiazepoxide withdrawal-induced anxiety in mice

Some antiepileptic drugs have been used with success to counteract withdrawal symptoms following chronic use of sedatives, hypnotics or alcohol. We evaluated the potential of levetiracetam (Keppra), a new antiepileptic drug, to prevent benzodiazepine withdrawal in an animal model sensitive to the anxiogenic effect resulting from drug cessation. The effects of levetiracetam (17 and 54 mg/kg) given intraperitoneally (i.p.) were determined on anxiety induced in female NMRI mice by withdrawal from 21 days of chronic administration of chlordiazepoxide. Administration of chlordiazepoxide was i.p. twice daily, in increments of 2 mg/kg, from 10 up to 40 mg/kg. Anxiety was evaluated using an elevated plus-maze test 24-h after chlordiazepoxide withdrawal. Discontinuation of chronic chlordiazepoxide induced a significant anxiogenic profile in the plus-maze test mainly characterised by a decrease in open arm exploration. This effect was dose-dependently prevented by administration of levetiracetam during the withdrawal period. The highest dose tested (54 mg/kg) induced statistically significant effects on all variables recorded but had no effect upon plus-maze exploration in normal mice. This suggests that the observed effects are dependent upon the level of stress or anxiety of the animals. These results support potential efficacy of levetiracetam in the benzodiazepine withdrawal syndrome.     

Neurochemically dissimilar anxiolytic drugs have common effects on hippocampal rhythmic slow activity.

Previous experiments have shown that anxiolytic drugs reduce the frequency of hippocampal rhythmic slow activity, induced by high frequency stimulation of the reticular formation and flatten the function relating threshold septal stimulation to the frequency of driven rhythmic slow activity. All of the drugs involved are known to augment GABAergic transmission. The present experiments investigated the effects of the novel anxiolytic compound buspirone which, unlike conventional anxiolytics, does not interact with GABA, yet is a clinically effective anxiolytic. Buspirone (0.156-40 mg/kg, i.p.) was found to reduce the frequency of reticular-elicited rhythmic slow activity, in a similar manner to chlordiazepoxide (0.019-20 mg/kg, i.p.). Buspirone did not change the linearity of the voltage-frequency function. Buspirone (10 mg/kg, i.p.) also altered the threshold for septal driving of rhythmic slow activity, in a similar manner to classical anxiolytics. The combination of chlordiazepoxide (5 mg/kg, i.p.) with corticosterone (0.2 mg, s.c.) removed the minor differences between buspirone and chlordiazepoxide in both the septal and reticular tests. These results show that buspirone altered the control of rhythmic slow activity in the hippocampus, in a manner which appeared functionally equivalent to other anxiolytics but which depends on mechanisms which are likely to be neurally and pharmacologically distinct from those of other anxiolytic drugs.     

Abecarnil, a β-carboline derivative, does not exhibit anticonvulsant tolerance or withdrawal effects in mice

Development of tolerance and dependence has been reported to occur upon chronic administration of traditional benzodiazepines (BZDs). We compared the effect of chronic treatment with abecarnil, a -carboline derivative with high affinity for central BDZ receptors, and diazepam, the BDZ prototype, in mice.After acute administration, abecarnil was as potent and effective as diazepam in protecting from bicuculline-induced convulsion. The time-course analysis of two peak equieffective doses of abecarnil (1.9 mg/kg p.o.) and diazepam (2.7 mg/kg p.o.) showed a similar duration of action. The anticonvulsant potency of diazepam was reduced in mice given chronic diazepam (25 mg/kg p.o., 2 times a day for 17 days). No tolerance to abecarnil was apparent when the drug was administered for the same period using a comparable dose (20 mg/kg p.o.). Severe symptoms of precipitated withdrawal were observed upon administration of the BDZ partial inverse agonist Ro 15-3505 in mice treated chronically with diazepam but not abecarnil. In mice made tolerant to diazepam, maximum [³H]-flumazenil binding sites were reduced in both cerebral cortex (–50%) and cerebellum (–55.2%). No changes in [³H]-flumazenil binding were measured in chronic abecarnil-treated mice.These data indicate that abecarnil possesses a very low tolerance/dependence liability and does not affect BZD receptor density after chronic administration.     

The sedative effects of CL 218,872, like those of chlordiazepoxide,are reversed by benzodiazepine antagonists

The effects of CL 218,872, initially classified as a non-sedative anxiolytic, were investigated and compared with those of chlordiazepoxide in the holeboard. The ability of two drugs that antagonise the effects of benzodiazepines, CGS 8216 and Ro 15-1788, to reverse the effects of CL 218,872 and chlordiazepoxide were also investigated, to see whether their effects might be mediated via benzodiazepine receptors. CL 218,872 (10 mg/kg) was found to be significantly sedative in both mice and rats (i.e., both locomotor activity and head-dipping were significantly decreased). In mice, the effects of CL 218,872 and of chlordiazepoxide were very similar over a range of doses, except that the stimulatory effect seen with low doses of chlordiazepoxide on head-dipping just failed to reach significance with CL 218,872. This study is in agreement with recently published results from different tests showing that sedative effects can be obtained with doses of CL 218,872 that are low and not much higher than those leading to anxiolysis. The sedative effects of both CL 218,872 (10 mg/kg) and chlordiazepoxide (20 mg/kg) were significantly reversed by RO 15-1788 (10 and 20 mg/kg) and CGS 8216 (10 mg/kg), suggesting that their effects are mediated via benzodiazepine receptors. The increase in head-dipping seen with chlordiazepoxide (2.5 mg/kg) was also reversed by RO 15-1788 and CGS 8216.     

Effects of the brain-penetrant and selective 5-HT6 receptor antagonist SB-399885 in animal models of anxiety and depression

The effects of a selective 5-HT(6) receptor antagonist, SB-399885 (N-[3,5-dichloro-2-(methoxy)phenyl]-4-(methoxy)-3-(1-piperazinyl)benzenesulfonamide), were evaluated in behavioural tests sensitive to clinically effective anxiolytic- and antidepressant-compounds using diazepam and imipramine as reference drugs. In the Vogel conflict drinking test in rats, SB-399885 (1-3mg/kg i.p.) caused an anxiolytic-like activity comparable to that of diazepam (2.5-5mg/kg i.p.). An anxiolytic-like effect was also seen in the elevated plus-maze test in rats, where SB-399885 (0.3-3mg/kg i.p.) was slightly weaker than diazepam (2.5-5mg/kg i.p.). In the four-plate test in mice, SB-399885 (3-20mg/kg i.p.) showed an anxiolytic-like effect which was weaker than that produced by diazepam (2.5-5mg/kg i.p.). In the forced swim test in rats, SB-399885 (10mg/kg i.p.) significantly shortened the immobility time and the effect was stronger than that of imipramine (30mg/kg i.p.). In the forced swim test in mice, SB-399885 (20-30mg/kg i.p.) had an anti-immobility action, comparable to imipramine (30mg/kg i.p.) and also in the tail suspension test in mice, SB-399885 (10-30mg/kg i.p.) had an antidepressant-like effect, though was weaker than imipramine (10-20mg/kg i.p.). The tested 5-HT(6) antagonist (3-20mg/kg i.p.) shortened the walking time of rats in the open field test and, at a dose of 30mg/kg i.p. reduced the locomotor activity of mice. SB-399885 (in doses up to 30mg/kg i.p.) did not affect motor coordination in mice and rats tested in the rota-rod test. Such data indicate that the selective 5-HT(6) receptor antagonist SB-399885had specific effects, indicative of this compound's anxiolytic and antidepressant potential.     

Continuous slow release of low levels of diazepam produces tolerance to its depressant and anxiolytic effects on the startle reflex

Development of tolerance to the depressant effects of diazepam on the acoustic startle reflex and to the blockade of fear-potentiated startle, a measure of fear or anxiety in rodents, was evaluated after chronic administration via continuous release from implanted diazepam-filled silastic capsules or daily intraperitoneal (i.p.) injections. After continuous exposure to diazepam via capsule implants, complete tolerance occurred to the depressant effects of diazepam on startle and partial tolerance occurred to the antifear effects. In contrast, no tolerance was observed after daily i.p. injection with comparable amounts of diazepam (5 mg/kg) although tolerance could be produced by daily i.p. injections of a much higher dose of diazepam (20 mg/kg). These data suggest that tolerance to at least some behavioral effects may be much easier to produce with continuous rather than intermittent occupation of benzodiazepine receptors.